1. Field of the Invention
The present invention relates to a medical device and more specifically, to a anchor device which is adapted to facilitate the positioning of an ablation element at a location where a pulmonary vein extends from the left atrial wall.
2. Description of the Related Art
Cardiac arrhythmia""s, particularly atrial fibrillation, are a pervasive problem in modem society. Although many individuals lead relatively normal lives despite persistent atrial fibrillation, the condition is associated with an increased risk of myocardial ischemia, especially during strenuous activity. Furthermore, persistent atrial fibrillation has been linked to congestive heart failure, stroke, and other thromboembolic events. Thus, atrial fibrillation is a major public health problem.
Normal cardiac rhythm is maintained by a cluster of pacemaker cells, known as the sinoatrial (xe2x80x9cSAxe2x80x9d) node, located within the wall of the right atrium. The SA node undergoes repetitive cycles of membrane depolarization and repolarization, thereby generating a continuous stream of electrical impulses, called xe2x80x9caction potentials.xe2x80x9d These action potentials orchestrate the regular contraction and relaxation of the cardiac muscle cells throughout the heart. Action potentials spread rapidly from cell to cell through both the right and left atria via gap junctions between the cardiac muscle cells. Atrial arrhythmia""s result when electrical impulses originating from sites other than the SA node are conducted through the atrial cardiac tissue.
In most cases, atrial fibrillation results from perpetually wandering reentrant wavelets, which exhibit no consistent localized region(s) of aberrant conduction. Alternatively, atrial fibrillation may be focal in nature, resulting from rapid and repetitive changes in membrane potential originating from isolated centers, or foci, within the atrial cardiac muscle tissue. These foci exhibit consistent centrifugal patterns of electrical activation, and may act as either a trigger of atrial fibrillatory paroxysmal or may even sustain the fibrillation. Recent studies have suggested that focal arrhythmia""s often originate from a tissue region along the pulmonary veins of the left atrium, and even more particularly in the superior pulmonary veins.
Several surgical approaches have been developed for the treatment of atrial fibrillation. For example, Cox, J L et al. disclose the xe2x80x9cmazexe2x80x9d procedure, in xe2x80x9cThe Surgical Treatment Of Atrial Fibrillation. I. Summaryxe2x80x9d, Thoracic and Cardiovascular Surgery 101(3):402-405 (1991) and xe2x80x9cThe Surgical Treatment Of Atrial Fibrillation. IV. Surgical Techniquexe2x80x9d, Thoracic and Cardiovascular Surgery 101(4):584-592 (1991). In general, the maze procedure is designed to relieve atrial arrhythmia by restoring effective SA node control through a prescribed pattern of incisions about the cardiac tissue wall. Although early clinical studies on the maze procedure included surgical incisions in both the right and left atrial chambers, more recent reports suggest that the maze procedure may be effective when performed only in the left atrium (see for example Sueda et al., xe2x80x9cSimple Left Atrial Procedure For Chronic Atrial Fibrillation Associated With Mitral Valve Diseasexe2x80x9d (1996)).
The left atrial maze procedure involves forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the inferior pulmonary veins en route. An additional horizontal incision connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the atrial arrhythmia by blocking conduction of the aberrant action potentials.
The moderate success observed with the maze procedure and other surgical segmentation procedures have validated the principle that mechanically isolating cardiac tissue may successfully prevent atrial arrhythmia""s, particularly atrial fibrillation, resulting from either perpetually wandering reentrant wavelets or focal regions of aberrant conduction. Unfortunately, the highly invasive nature of such procedures may be prohibitive in many cases. Consequently, less invasive catheter-based approaches to treat atrial fibrillation through cardiac tissue ablation have been developed.
These less invasive catheter-based therapies generally involve introducing a catheter within a cardiac chamber, such as in a percutaneous translumenal procedure, wherein an energy sink on the catheter""s distal end portion is positioned at or adjacent to the aberrant conductive tissue. Upon application of energy, the targeted tissue is ablated and rendered non-conductive.
The catheter-based methods can be subdivided into two related categories, based on the etiology of the atrial arrhythmia. First, focal arrhythmias have proven amenable to localized ablation techniques, which target the foci of aberrant electrical activity. Accordingly, devices and techniques have been disclosed which use end-electrode catheter designs for ablating focal arrhythmia""s centered in the pulmonary veins, using a point source of energy to ablate the locus of abnormal electrical activity. Such procedures typically employ incremental application of electrical energy to the tissue to form focal lesions.
The second category of catheter-based ablation methods is designed for treatment of the more common forms of atrial fibrillation, resulting from perpetually wandering reentrant wavelets. Such arrhythmias are generally not amenable to localized ablation techniques, because the excitation waves may circumnavigate a focal lesion. Thus, the second class of catheter-based approaches have generally attempted to mimic the earlier surgical segmentation techniques, such as the maze procedure, wherein continuous linear lesions are required to completely segment the atrial tissue so as to block conduction of the reentrant wave fronts.
For the purpose of comparison, ablation catheter devices and related methods have also been disclosed for the treatment of ventricular or supraventricular tachycardias, such as disclosed by Lesh, M D in xe2x80x9cInterventional Electrophysiologyxe2x80x94State Of The Art, 1993xe2x80x9d American Heart Journal, 126:686-698 (1993) and U.S. Pat. No. 5,231,995 to Desai.
An example of an ablation method targeting focal arrhythmia""s originating from a pulmonary vein is disclosed by Haissaguerre et al. in xe2x80x9cRight And Left Atrial Radiofrequency Catheter Therapy Of Paroxysmal Atrial Fibrillationxe2x80x9d in J. Cardiovasc. Electrophys. 7(12):1132-1144 (1996). Haissaguerre et al. describe radiofrequency catheter ablation of drug-refractory paroxysmal atrial fibrillation using linear atrial lesions complemented by focal ablation targeted at arrhythmogenic foci in a screened patient population. The site of the arrhythmogenic foci was generally located just inside the superior pulmonary vein, and was ablated using a standard 4 mm tip single ablation electrode.
Another ablation method directed at paroxysmal arrhythmia""s arising from a focal source is disclosed by Jais et al. xe2x80x9cA Focal Source Of Atrial Fibrillation Treated By Discrete Radiofrequency Ablationxe2x80x9d Circulation 95:572-576 (1997). At the site of arrhythmogenic tissue, in both right and left atria, several pulses of a discrete source of radiofrequency energy were applied in order to eliminate the fibrillatory process.
Application of catheter-based ablation techniques for treatment of reentrant wavelet arrhythmia""s demanded development of methods and devices for generating continuous linear lesions, like those employed in the maze procedure. Initially, conventional ablation tip electrodes were adapted for use in xe2x80x9cdrag burnxe2x80x9d procedures to form linear lesions. During the xe2x80x9cdragxe2x80x9d procedure, as energy was being applied, the catheter tip was drawn across the tissue along a predetermined pathway within the heart. Alternatively, sequentially positioning the distal tip electrode, applying a pulse of energy, and then re-positioning the electrode along a predetermined linear pathway also made lines of ablation.
Subsequently, conventional catheters were modified to include multiple electrode arrangements. Such catheters typically contained a plurality of ring electrodes circling the catheter at various distances extending proximally from the distal tip of the catheter. More detailed examples of such catheter-based tissue ablation assemblies have been disclosed in U.S. Pat. No. 5,676,662 to Fleischhacker et al.; U.S. Pat. No. 5,688,267 to Panescu et al.; and U.S. Pat. No. 5,693,078 to Desai et al.
Examples of catheter-based cardiac chamber segmentation procedures, particularly in the treatment of Wolff-Parkinson-White syndrome, are disclosed by Avitall et al. xe2x80x9cPhysics And Engineering Of Transcatheter Tissue Ablationxe2x80x9d J. Am. College of Cardiology, 22(3):921-932 (1993) and Haissaguerre et al. xe2x80x9cRight And Left Atrial Radiofrequency Catheter Therapy Of Paroxysmal Atrial Fibrillationxe2x80x9d J. Cardiovasc. Electrophys. 7(12):1132-1144 (1996).
Further more detailed examples of transcatheter-based tissue ablation assemblies and methods are described in the following references: U.S. Pat. No. 5,575,810 to Swanson et al.; PCT Published Application WO 96/10961 to Fleischman et al.; U.S. Pat. No. 5,702,438 to Avitall; U.S. Pat. No 5,687,723 to Avitall; U.S. Pat. No. 5,487,385 to Avitall; and PCT Published Application WO 97/37607 to Schaer.
While the disclosures above describe feasible catheter designs for imparting linear ablation tracks, as a practical matter, most of these catheter assemblies have been difficult to position and maintain placement and contact pressure long enough and in a sufficiently precise manner in the beating heart to successfully form segmented linear lesions along a chamber wall. Indeed, many of the aforementioned methods have generally failed to produce closed transmural lesions, thus leaving the opportunity for the reentrant circuits to reappear in the gaps remaining between point or drag ablations. In addition, minimal means have been disclosed in these embodiments for steering the catheters to anatomic sites of interest such as the pulmonary veins. Subsequently, a number of attempts to solve the problems encountered with precise positioning, maintenance of contact pressure, and catheter steering have been described. These include primarily the use of (1) preshaped ablating configurations, (2) deflectable catheter assemblies, and (3) transcatheter ablation assemblies.
None of the catheter-based ablation assemblies have included a balloon anchor wire for positioning and anchoring one end of an elongated ablation member within the ostium of a pulmonary vein. Nor does the prior art disclose a method for securing the ablation member between a first and second anchor, thereby maintaining a desired linear position in contact with the atrial wall and facilitating the formation of a linear ablation track along the length of tissue between the anchors.
The present invention relates to a tissue ablation system for ablating a region of tissue at the location where a pulmonary vein extends from an atrium in a patient. The tissue ablation system includes an anchor device adapted to be positioned within the pulmonary vein and an ablation device. The anchor device has an elongate body with a proximal end portion and a distal end portion. It also has an expandable member along the distal end portion that is adjustable between a radially collapsed condition and a radially expanded condition that is adapted to engage the pulmonary vein. The ablation device comprises an elongate catheter having a proximal region and a distal region. The ablation device has an ablation element located along the distal region, wherein the ablation device is adapted to slideably engage and track over the anchor device. By advancing the ablation device distally over the anchor device, which is positioned in the pulmonary vein, the ablation element can be positioned at the region of tissue to be ablated.
In one preferred mode of the tissue ablation system, the expandable member is an inflatable balloon. The elongate body may also comprise an inflation lumen, a pressurizable fluid source and a removable adapter on the proximal end portion of the elongate body. The adapter is adapted to couple the pressurizable fluid source to the inflation lumen. The balloon has an outer diameter of from about 0.114xe2x80x3 to about 0.122xe2x80x3 when inflated. The balloon may be made from any low density polymers or copolymers known in the art, such as polyethylene, polypropylene, polyolefins, PET, nylon, urethane, silicon, or Cflex. The polymeric material is preferably an irradiated linear low-density polyethylene.
In accordance with another variation, the anchor device of the tissue ablation system may have a shaped distal tip distal of the expandable member. Preferably, the anchor device is torquable and steerable, such that the anchor device may be directed into the pulmonary vein by manipulation of the proximal end portion. The elongate body of the anchor device comprises a polymeric tube.
The elongate body of the anchor device may be more flexible in the distal end portion than the proximal end portion. Also, the elongate body may have an intermediate region between the distal and proximal end portions, wherein the wall thickness of the proximal end portion is greater than the wall thickness of the intermediate region, such that the proximal end portion possess sufficient push force and kink resistance.
In one preferred mode, the anchor device also comprises a wire within the elongate body. The wire may extend proximally from the distal end portion of the elongate body through at least a portion of the elongate body. In a variation to the present aspect, the elongate body may also have a guidewire passageway, wherein the wire is a guidewire slideably engaged in the guidewire passageway. The guidewire passageway may have a proximal port along the proximal end portion of the elongate body and a distal port along the distal end portion of the elongate body. In another variation, the guidewire passageway may extend only through a portion of the elongate body.
The ablation elements employed in different modes of the tissue ablation system can comprise a microwave ablation element, a cryogenic ablation element, a thermal ablation element, a light-emitting ablation element (e.g., laser), an ultrasound transducer, or an electrical ablation element, such as an RF ablation element.
In a variation of the tissue ablation system of the present aspect, the ablation element may be adapted to form a linear lesion. In addition or in the alternative, the ablation element may be adapted to form a circumferential lesion, which may be formed at the location where a pulmonary vein extends from the left atrium.
Another aspect of the present invention includes a positioning system adapted to position and anchor one end of a medical device at a location where a pulmonary vein extends from the left atrium. The positioning system has a transeptal sheath which is inserted through the atrial septum that separates the right atrium from the left atrium. The positioning system also has an anchor device adapted to be positioned within the pulmonary vein. The anchor device has an elongate body with a proximal end portion and a distal end portion, and also has an expandable member along the distal end portion that is adjustable between a radially collapsed condition and a radially expanded condition that is adapted to engage the pulmonary vein.
The medical device preferably has a tracking mechanism adapted to slideably engage and track over the anchor device, such that advancing the medical device over the anchor device causes one end of the medical device to be positioned at the location where the pulmonary vein extends from the atrium. In one variation, the medical device is a mapping device with an electrode adapted to map a region of tissue at the location. In another variation, the medical device is an ablation device having an ablation element adapted to ablate a region of tissue at the location.
In modes where the medical device is an ablation device, the ablation element may be a microwave ablation element, a cryogenic ablation element, a thermal ablation element, a light-emitting ablation element, an ultrasound transducer, or an electrical ablation element, such as an RF ablation element.
In a variation of the tissue ablation system of the present aspect, the ablation element may be adapted to form a linear lesion. In addition or in the alternative, the ablation element may be adapted to form a circumferential lesion, which may be formed at the location where a pulmonary vein extends from the left atrium.
In one preferred mode of the positioning system, the expandable member is an inflatable balloon. In the present aspect, the elongate body may also comprise an inflation lumen, a pressurizable fluid source and a removable adapter on the proximal end portion of the elongate body. The adapter is adapted to couple the pressurizable fluid source to the inflation lumen. The balloon has an outer diameter of from about 0.114xe2x80x3 to about 0.122xe2x80x3 when inflated. The balloon may be made from any low density polymers or copolymers known in the art, such as polyethylene, polypropylene, polyolefins, PET, nylon, urethane, silicon, or Cflex.
In accordance with another variation of the positioning system, the anchor device of the tissue ablation system may have a shaped distal tip distal of the expandable member. Preferably, the anchor device is torquable and steerable, such that the anchor device may be directed into the pulmonary vein by manipulation of the proximal end portion. The elongate body of the anchor device comprises a polymeric tube.
The elongate body of the anchor device may be more flexible in the distal end portion than the proximal end portion. Also, the elongate body may have an intermediate region between the distal and proximal end portions, wherein the wall thickness of the proximal end portion is greater than the wall thickness of the intermediate region, such that the proximal end portion possess sufficient push force and kink resistance.
In one preferred mode of the positioning system, the anchor device also comprises a wire within the elongate body. The wire may extend proximally from the distal end portion of the elongate body through at least a portion of the elongate body. In a variation to the present aspect, the elongate body may also have a guidewire passageway, wherein the wire is a guidewire slideably engaged in the guidewire passageway. The guidewire passageway may have a proximal port along the proximal end portion of the elongate body and a distal port along the distal end portion of the elongate body. In another variation, the guidewire passageway may extend only through a portion of the elongate body.
The present invention is also related to a method of ablating a region of tissue at a location where the pulmonary vein extends from the left atrium. The method comprises the steps of: inserting into the atrium an anchor device adapted to be positioned within the pulmonary vein and having an elongate body with a proximal end portion and a distal end portion, and also having an expandable member along the distal end portion; positioning the anchor device within the pulmonary vein; anchoring the distal end portion of the anchor device within the pulmonary vein by adjusting the expandable member from the radially collapsed condition to the radially expanded condition; providing an ablation catheter adapted to slideably engage and track over the anchor device and also having an ablation element adapted to couple to an ablation actuator; advancing the ablation catheter into the atrium over the anchor device until the ablation element is positioned at the location; actuating the ablation actuator to energize the ablation element; and ablating the region of tissue with the ablation element.
In a variation of the method, prior to inserting the anchor device, a transeptal sheath is inserted through the atrial septum that separates the right atrium from the left atrium. In a further variation of the method, a guide member having a preshaped distal portion may be inserted through the transeptal sheath from the right atrium into the left atrium, prior to inserting the anchor device. In still a further variation of the method, the preshaped distal portion of the guide member may be positioned within the left atrium so that it points toward the pulmonary vein, and the anchor device is then inserted into the left atrium through the guide member. In one preferred variation of the method, the guide member is removed prior to advancing the ablation catheter over the anchor device.